1. Field of the Invention
The present invention relates to a signal processing device for supplying a drive voltage signal to a display panel having two opposing substrates provided with electrodes, at least one of the substrates being transparent, and having a plurality of display elements arranged along a predetermined scanning line which are driven by the drive voltage signal applied between the electrodes. The present invention also relates to a signal processing method.
2. Description of Related Art
A general liquid crystal display panel includes a plurality of liquid crystal elements, each composed of pixel electrodes mounted on a first substrate, a common electrode mounted on a second substrate opposed to the first substrate, and a dielectric anisotropic liquid crystal layer held between the pixel electrodes and the common electrode. Each liquid crystal element changes the transmittance of light passing through the liquid crystal layer by changing the strength of the electric field between the pixel electrodes and the common electrodes in response to the voltage level of a drive voltage signal. The liquid crystal display panel is driven to display a desired image on the respective liquid crystal elements by adjusting the voltage levels applied to the pixel electrodes and the common electrode, respectively.
In such a liquid crystal display panel, the high luminance and high resolution of display images can be attained by decreasing the distance between the adjacent liquid crystal elements within the panel. However, the following problem may occur when the distance between the adjacent liquid crystal elements is decreased in the liquid crystal display panel. That is, depending on the voltage level difference between the drive voltage signals supplied to the adjacent liquid crystal elements, the electric field disturbance occurs at the liquid crystal layer and the light transmittance is changed correspondingly, thus deteriorating the quality of images to be displayed.
Among various liquid crystal display panels, a single-panel type liquid crystal display panel in which liquid crystal elements for displaying red light, liquid crystal elements for displaying green light, and liquid crystal elements for displaying blue right are arranged along a scanning line has different characteristics in the liquid crystal layers of the adjacent liquid crystal elements. As a result, the electric field disturbance causes on the respective liquid crystal elements, as shown in FIGS. 11A and 11B.
FIGS. 11A and 11B show schematically the cross-sectional shapes of the single-plate type liquid crystal display panel, in which liquid crystal elements G for displaying green light, liquid crystal elements B for displaying blue light, and liquid crystal elements R for displaying red light are arranged along the scanning line, respectively. FIGS. 11A and 11B also show schematically curves E1 and E2 indicating the electric field strength according to the position of the scanning line, together with the liquid crystal orientation in the individual liquid crystal elements. These liquid crystal elements arranged in the liquid crystal display panel are designed so that the luminance level is lowered from the maximum value to the minimum value as the voltage value applied is changed from 0V to 5V.
The liquid crystal display panel is usually set so as to achieve a good white display. Therefore, upon the application of the voltage of, for example, 2V to all of the liquid crystal elements G, B, and R, as represented by the curve E1 in FIG. 11A, the orientations of the entire liquid crystal layers of the respective liquid crystal elements can be changed substantially uniformly so that the pixels corresponding to these liquid crystals can display the desired gray.
However, when the drive voltage level applied to the liquid crystal elements G is set to 5V, and the drive voltage levels applied to the liquid crystal elements R and B adjacent to the liquid crystal element G are set to 2V, respectively, as represented by the curve E2 in FIG. 11B, the electric field disturbance occurs at the respective liquid crystal elements of the liquid crystal display panel due to the following causes.
Specifically, due to the influence of the electric field of the liquid crystal element G adjacent to the reverse direction of the scanning line, the liquid crystal elements B shown in FIG. 11B have lower electric field strength at a range W1 adjacent to the liquid crystal element G, than the liquid crystal element B shown in FIG. 11A. Consequently, the pixel luminance level to be displayed by the liquid crystal element B shown in FIG. 11B is higher than that displayed by the liquid crystal element B shown in FIG. 11A. On the other hand, due to the influence of the electric field of the liquid crystal element G adjacent to the forward direction of the scanning line, the liquid crystal element R shown in FIG. 11B have higher electric field strength at a range W2 adjacent to the liquid crystal element G, than the liquid crystal elements B shown in FIG. 11A. Consequently, the pixel luminance level to be displayed by the liquid crystal element R shown in FIG. 11B is higher than that displayed by the liquid crystal element G shown in FIG. 11A.
The degree to which the liquid crystal orientation is disturbed by the electric field strength of the adjacent liquid crystal elements becomes higher with decreasing the distance between the adjacent liquid crystal elements, particularly.
Japanese Unexamined Patent Application Publication No. 2005-352443 discloses a liquid crystal display apparatus that corrects the luminance level of a pixel by referring to the luminance level of the adjacent pixel along the scanning line of the pixel. In the liquid crystal display apparatus, for example, the luminance level of the liquid crystal element B shown in FIG. 10B cannot be corrected properly because the correction is made by referring to the luminance level of the pixel adjacent to one direction, in other words, the correction is not made by referring to the luminance level of the pixel adjacent to the reverse direction of the scanning line.
Japanese Unexamined Patent Application Publication No. 2000-321559 discloses a display apparatus that corrects the image signal of a pixel by referring to the image signals of two adjacent pixels in the forward and reverse directions of the scanning line of the pixel, respectively. In the display apparatus, the correction is made by considering similarly the influences of the adjacent pixels, irrespective of whether the adjacent pixel is positioned in the forward or reverse direction with respect to the pixel. Accordingly, when the array of the liquid crystal elements within the panel is laterally asymmetric, and when the liquid crystal elements control the liquid crystal orientation including the tilt angle, the degree to which the liquid crystal orientation is disturbed by the voltage level difference between the adjacent liquid crystal elements varies depending on the direction in which the adjacent pixel is adjacent. It is therefore difficult to properly correct the luminance level.
As the display panel having two opposing substrates provided with electrodes, at least one of the substrates being transparent, and having a plurality of display elements arranged along a predetermined scanning line which are driven by the drive voltage signal applied between the electrodes, there are, besides the liquid crystal display panels described above, those in which the luminance level displayed by a display element vary depending on the signal level of a drive voltage signal supplied to the adjacent display element.